Due to the ability of cationic functionality of polymer to hydrogen bond with cellulose fibers, polymers containing amine functionality are well studied in paper industry. Use of cationic polymer has proven improvement in paper strength, drainage, retention and several other properties. Several patents and research articles discusses use of polyvinylamine as a paper making additive. U.S. Pat. No. 2,721,140 discloses use of polyvinylamine as an additive to make papers having high wet strength, while U.S. Pat. No. 5,961,782 discloses use of polyvinylamine to make crosslinkable creping adhesive formulations.
Among the polymers with amine functionality, the cost effective synthesis of polymer containing primary amine functionality has been a challenge for generations. The monomers that can introduce primary amine functionality, on polymerization are allylamine and vinylamine (VAm) or, on hydrolysis are vinylformamide (VFA) and vinyl acetamide. Due to lack of conjugation in allylamine and presence of free amine functionality, polymerization of allylamine is relatively sluggish and also leads in several side reactions like inhibition or chain transfer. Therefore, it is challenging to synthesize allylamine containing polymers with high molecular weight. Whereas, vinyl amine monomer does not exist in free state, and hence it was not possible to synthesize polyvinylamine. The significant efforts by the Air Products and Chemicals Inc., BASF and DiaNitrix resulted in vinylformamide monomer. BASF launched the industrial production of vinylformamide (VFA) momomer that can be effectively polymerized by using radical initiators to synthesize materials with high molecular weight. VFA homopolymers as well VFA copolymers with vinyl monomers offers a material with distinctive chemical and physical properties. The hydrolysis of poly(VFA) results in a material with pendant primary amine functionality that makes these polymers highly cationic in nature. The introduction of primary amine functionality on alternate carbon atoms yields the material with a relatively high charge density and cationicity that makes this material as an attractive and viable candidate for variety of commercial applications. U.S. Pat. No. 4,421,602 discloses a partially hydrolyzed, water-soluble polymer of n-vinylformamide that contains n-vinylformamide units and vinylamine units. It also discloses use of polyvinylamine and a 50% hydrolyzed polyvinylformamide to increase flocculation efficiencies, fines retention, and the drainage rate of pulp fiber in papermaking processes, while U.S. Pat. No. 6,159,340 discloses the use of such polymers as dry and wet strength additives in paper and paperboard production. U.S. Pat. Nos. 6,616,807 and 6,797,785 disclose use of polyvinylamines as drainage aids, flocculants, and retention aids in the paper making.
Vinylformamide copolymers and their subsequently hydrolyzed products are also known additives for paper applications. U.S. Pat. No. 4,774,285 discloses that n-vinylformamide monomer may be copolymerized with an additional vinyl monomer, e.g., vinyl acetate, and subsequently hydrolyzed to produce a water-soluble copolymer of vinylamine and vinyl alcohol, which may be used as wet and dry strength additives for papermaking. U.S. Pat. No. 5,630,907 discloses copolymer compositions containing vinyl amine and acrylic acid units, as well as their applications. U.S. Pat. No. 6,797,785 discloses copolymers containing vinylamine units in combination with either diallyldimethylammonium (chloride) (DADMAC) or acrylamide units via reverse emulsion polymerization, and their use as flocculants and coagulants in papermaking. EP 0251182 discloses copolymers containing vinylamine and acrylonitrile units for use in papermaking as drainage aids, retention aids, as well as wet end additives for increasing the dry strength of paper products.
Styrene containing polymers are also well utilized in a variety of applications, due to their relatively low cost, and compatibility with other polymers. The aromatic group of styrene offers unique properties to the material namely, better hydrophobicity, higher thermal stability, and resistance to acid or base conditions during hydrolysis. U.S. Pat. No. 4,328,579 discloses copolymerization of n-vinyl acetamide with styrene and substituted styrene and its subsequent hydrolysis to form styrene-vinyl amine copolymer. However, the copolymerization reactions are slow and need almost 57 hours to achieve 96% conversion. Additionally the polymer needs to be purified by precipitation in a non-solvent to remove residual monomer, and the soluble nature of the material suggests the obtained polymers have a relatively low molecular weight. On the other hand attempts to copolymerize styrene with VFA resulted in lower conversions and lower molecular weight material. (Journal of Polymer Science Part A: Polymer Chemistry, 2010, 48, 2257-2283).
Therefore, it is desirable to develop a polymerization process to copolymerize styrene with VFA with high efficiency of shorter reaction time resulting in high conversion of the monomers into the polymer products without further purification. It is also desirable to produce a cationic copolymer containing VAm, VFA, and styrene groups, which can be used as a cost effective dry strength additive in papermaking and has many other potential applications.